Voltage generating apparatus



Sept. 17, 1940.

w. F. WESTEN'DIORP 2,214,871

VOLTAGE GENERATING APPARATUS Filed Aug. 27, 1938 Sheets-Sheet l i A /m vv A Ce mm 06F07'E/1/77/1L CONDENSER VOL746 Cg J6,

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Willem F. Wescendorp,

H is Attorney.

p 1940- w. F. WESTENDORP 2,214,871

VOLTAGE GENERATING APPARATUS Filed Aug. 27, 193.8 2 Sheets-Sheet 2Inventor: Wi I learn F. Westendorp,

i Attorney.

Patented Sept. 17, 19 40 UNITE STAi'Efi VOLTAGE GENERATING APPARATUSWillem F. Westendorp, Schenectady, N. Y., assignor to General ElectricCompany, a corporation of New York Application August 27, 1938, SerialNo. 227,223

8 Claims.

The present invention relates to static apparatus for generatingunidirectional potentials.

It is an object of the invention to provide means whereby a constantpotential of great magnitude can be derived from an alternatingpotential source of low intensity. The new apparatus involves thecombination of a resonant oscillating circuit with means for causingvoltages developed in the circuit to appear as a constant potentialacross appropriate terminals. The system provided has a substantialadvantage over systems heretofore available in requiring relativelysimple and inexpensive apparatus. It is particularly noteworthy thatwhere the system is to be used for high voltage purposes, it can utilizea large number of relatively low tension elements each of which sustainsonly a proportionate share of the total load.

The novel features which I desire to protect herein are pointed out inthe appended claims. The invention itself, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description taken in connection with the accompanyingdrawings, in which Fig. 1 illustrates diagrammatically one embodiment ofthe invention; Fig. 2 is a vector diagram useful in explaining theinvention; Figs. 3, 4a, 4b and 4c are graphical representations helpfulin describing the operation of the invention; and Figs. 5, 6, '7 and 8illustrate alternative applications thereof.

In Fig. 1 I have illustrated the application of my invention inconnection with a multisection X-ray tube of known character. Referringparticularly to the circuit elements which appear at the left hand sideof the figure it will be seen that they comprise a pair of similarcircuit branches each of which includes a plurality of elementalsub-groups. Each group in turn comprises a condenser and an inductanceelement which is adapted to resonate with the condenser at a particularfrequency. The inductances, which may advantageously be of the iron coretype, are numbered from 10 to 1'7 inclusive while the condensers arerespectively numbered from 18 to 25.

The two circuit branches referred to are connected in a closed circuitso as to have two common terminals; one at the bottom (1') and one atthe top (2'). As a means for exciting the circuit there is provided analternating voltage source 30 which is coupled to the circuit by meansof a transformer 3| having its secondary winding directly in circuitwith the condenser and inductance elements. This arrangement is notessential, however, and it should be understood that any other knownmeans of supplying exciting energy to the circuit may be employed. It isthe function of the source 30 to supply the losses which occur in theresonant circuit and in the load apparatus associated therewith. In thisconnection the potential of the source 30 may be quite low and need haveno special relationship to the total voltage desired to be generated bythe apparatus as a whole.

With the circuit elements as so far described, and ignoring for themoment the remaining illustrated parts of the apparatus, the potentialdistribution may be as indicated by the vector diagram of Fig. 2. Inthis figure the letters employed correspond to the terminals which areidentified by similar letters in Fig. 1. The diagram as a Whole isassumed to apply to the case where the circuit is energized at itsresonant frequency. From a consideration of the diagram it will be seenthat no point in the circuit attains a potential itith respect to anyother point appreciably greater than the value of the vector ab.(Actually the vector z'b, which is not shown in the drawings, wouldrepresent the greatest A. C. potential difference attainable in thesystem.) This is due to the fact that the voltage across a giveninductance and the successive condenser are practically out of phase.

The vectors ac, ce, etc., correspond to the components of voltagerequired to supply the power losses in the various circuit groups. Thesecomponents, which are supplied by the transformer 31, may be quite smallwith relation to the reactive voltages developed. For example, assumingthat twenty inductance elements and twenty condensers are provided andthat the voltage developed across each element is 100 kilovolts (peakvalue) for a current of 100 milliamperes (peak value) then an inputvoltage of only 20,000 volts peak would be required to supply a loss inthe circuit of 1,000 watts (i. e., 2,000 watts peak).

It will be noted that the point i is separated from the point r (that isfrom ground) by the insulation of several condensers in series. Assumingthat some means can be provided for giving each of the condensers aconstant charge of proper polarity, the possibility exists of developingat the point i a constant potential of appreciable magnitude. Thus, 20condensers, each with 100 kilovolts constant potential, would providetogether 1,000 kilovolts constant potential. My invention provides meansby which this result can actually be obtained.

Broadly, this is effected by the use of means connected to permitunidirectional charging of the condensers pertaining to those circuitgroups across which a constant potential is desired to be developed.Various arrangements of asymmetrically conductive devices may be usedfor this purpose and several such arrangements are shown in thedrawings.

Possibly the simplest connection is that shown in Fig. 1 wherein aseries of rectifiers or unidirectionally conducting elements numbered 35to 38 respectively are connected across the condensers l8, I9, 20, and2!. The rectifiers employed may be of any one of various known typessuch as a contact rectifier or a vacuum or gas-filled discharge device.With the arrangement shown each condenser will draw a charging currentuntil the anode of its associated rectifier no longer becomesappreciably positive with respect to the rectifier cathode during anyportion of the cycle. When this condition is attained the voltage acrossthe condenser is a D. C. voltage plus an A. C. voltage of the samemagnitude. The A. C. voltage is still neutralized by the voltage of theassociated inductance so that the overall voltage across each elementalcircuit group is a constant potential without A. C. ripple. Furthermore,the voltage across the series of successive groups is a constantpotential comprising the sum of the constituent voltages. The condensersin the left branch of the circuit, i. e., condensers 22, 23 24, and 25will automatically assume the same charge distribution as the shuntedcondensers provided their leakage is equal.

The potential relationships referred to will be better understood byreference to Fig. 3 in which the curve A represents graphically thevariations of the voltage of the point b with respect to point a. Thecurve B represents the similar variations of voltage of the point ciizith respect tob, that is to say of the voltage across the condenserl8. From these curves it will be seen that the inductance voltage variessymmetrically above and below the potential at a. However, due to thepresence of the shunting rectifier 35 the upper plate of the condenserl8 can never become appreciably positive with respect to the lowerplate. On the other hand, the upper plate can and will during certainperiods become negative with respect to the lower plate and duringcertain other periods can and. will come to zero potential with respectto the lower plate. During the period that the two plates of thecondenser l8 are at the same potential, the lower plate is at arelatively high negative potential with respect to point a due to thevoltage existing across the inductance l0. Similarly, at the time theupper plate attains its highest negative potential with respect to thelower plate the latter is at its highest attainable positive potentialwith respect to point a, due again to the phase relation of the voltageacross the inductance Ill. The net effect is that the upper plate of theconductor i8 is maintained at substantially constant negative potentialwith respect to point a, or, in other words, that the potential acrossthe elemental circuit group comprising the inductance I0 and thecondenser i8 is constant. To say the same thing in another way, thevoltage across the condenser is a D-c voltage having superimposedthereon an alternating current voltage of the same magnitude as the D-cvoltage. As far as the condenser and inductance in combination areconcerned, the alternating current voltage across the condenser isneutralized by the oppositely phased voltage simultaneously developedacross the inductance.

The resultant D--c potential with respect to ground appearing at thepoint 0 is represented by the horizontal line C of Fig. 3. The totalunidirectional potential developed aoross the circuit as a whole isrepresented by the line C1 which represents the sum of the constituentvoltages existing across the various condensers in series.

It will be seen that since the circuit in question is of the resonanttype the total voltage produced is independent of the voltage of thesupply source 30 or of the transformer 35. The total voltage is limitedonly by the resistance losses in the system and may reach a very greatmagnitude if these losses are supplied from an external source (i.e.,the source 36) It is furthermore to be noted that each of the elementalcircuit groups sustains only its proportionate share of the totalvoltage so that no great concentration of the voltage stress is producedacross any one element. Consequently no individual element needs to behighly insulated.

. The system described may be employed to energize any kind of loaddevice which requires constant undirectional potential. In the presentcase I have illustrated as a load device a multi-section X-ray tube Mlcomprising a cathode M and a target or anode 42. There are also provideda number of intermediate electrodes d3, 84, and 65 which serve tomaintain a desired distribution of voltage along the axis of the tube.Assuming that the various elemental sub-groups of the resonant circuitare of similar character the intermediate electrodes is, M, and 45 mayappropriately be energized by connection to the terminals provided forthese sub-groups as illustrated.

In operation the current which is caused to flow through the X-ray tube(it by means of the potential applied to its terminals finds acontinuous return path which may be traced through the rectifier 33, theinductance i3, rectifier 3 inductance l2, rectifier 36, inductance ll,rectifier 35, inductance it and transformer 35 to ground. The systemshown may be indefinitely extended as long as the circuit connectionsprovide a continuous path for the unidirectional load current and forthe charging current of the various condenser elements.

The operation of the invention in connection with a load device isillustrated graphically in Figs. 4a, 4b, and 4c. The first of theserepresents the load current, which may be assumed to be substantiallyconstant after it is once initiated. As a result of the loss of chargeby the condensers during the period of operation of the load device, asubstantial ripple may appear in the unidirectional potential existingacross the system. This is illustrated in Fig. 4c wherein theregions ofnegative slope correspond to the discharge periods of the condensers.The loss of charge is automatically supplied, however, during a portionof each cycle of the oscillation of the resonant circuit by the passageof current through the rectifiers 35, 35, 3? and 38. The nature of thisrestorative current is illustrated in Fig. 4b. It will be understoodthat the total integrated area of the current curves of Fig. 4b will bethe same as the area underlying the load current curve of Fig. 4a.

The amount of ripple or variation occurring in the unidirectionalpotential is a function of the capacity of the condensers utilized andmay be limited to a desired value by an appropriate choice ofcondensers. The magnitude of the ripple may also be decreased and itsfrequency doubled by supplying additional rectifying devices in shunt tothe condensers 22, 23, 24, and 25WhiCh are provided in the left handbranch of the resonant circuit. As previously pointed out, the systemdescribed may be extended by cascading a large number of elementalcircuit groups, so as to produce a very high unidirectional voltage. Inorder properly to insulate the high potential terminal of the systemfrom ground the apparatus as a whole may be enclosed in a suitablecasing and immersed in a high strength dielectric medium such asinsulating oil or gas.

Assuming that the circuit elements employed in the two circuit branchesare identical, precisely the same unidirectional voltage distributionwill be maintained along each branch. This is true especially if theleakage factors of the condensers employed in the left branch are equal.When this condition is fulfilled, it is apparent that correspondingpoints in the two branches are at the same potential. Consequently, inconnection with the inductance elements it is possible to utilize acommon iron core member for two corresponding elements. This arrangementis illustrated in Fig. 5 wherein parts corresponding to those alreadydescribed in connection with Fig. 1 are similarly numbered. It will beseen that in this case the inductance coils i8 and it are paired so asto share a common iron core, identified in the drawings by the numeral56. Similarly, commcn cores 5! and 52 are provided for the remaininginductance windings. This feature adds to the economy of the system inthat it permits the use of a light and inexpensive construction. Ifdesired, a common magnetic circuit may be used for all the inductanceelements provided proper insulation is provided between the variousparts of such circuit.

As a further consequence of the symmetry which exists between the twobranches of the resonant circuit it is possible to use the furtheralternative arrangement shown in Fig. 6 wherein only alternatecondensers of each branch are shunted by rectifiers. More specifically,in the right hand branch only the condensers l9 and 2| are shunted,while in the other branch shunting rectifiers 53 and 5d are provided forcondensers 22 and 24. In order to provide a continuous circuit for thecurrent which is to be drawn from the system by a load device,equipotential points of the two circuit branches are interconnected bychoke coils 55, 56, and 5". as shown. By this means a path for directcurrent is provided between the terminals 1' and i by means of thevarious inductance elements and rectifiers taken in connection with thechoke coils. The relatively high impedance of the choke coils foralternating currents of the frequency assumed to be developed in theresonant circuit prevents any short-circuiting effect as to suchcurrents. The operation of the circuit of Fig. 6 is substantiallyidentical with that of Fig. 1 except for the fact that the rippleappearing in the unidirectional potential developed between theterminals r and i will be of double frequency. This is due to the factthat the rectifiers in the two branches pass current during alternatehalf-cycles.

It is not necessary that the rectifying elements be applied directlyacross the condenser elements as long as a continuous path forunidirectional current is provided which will permit unidirectionalcharging of the condensers. An alternative arrangement for accomplishingthis result is illustrated in Fig. '7 wherein are provided a pluralityof rectifying devices $5, 65, B7 and 68 connected between the twocircuit branches. It will be noted that each rectifier is connected fromthe bottom plate of a condenser in one branch of the circuit to theupper plate of the corresponding condenser in the other branch of thecircuit. Consequently, a continuous though zig-zag path forunidirectional charging current for the various condensers may be tracedthrough the various rectifiers and'the inductance elements in circuittherewith. The operation of the circuit will, therefore, be generallysimilar to that of the arrangements previously described.

By referring again to curve B of Fig. 3 it will be realized that thepeak voltage developed across each condenser is twice the unidirectionalvoltage developed across the elemental circuit group with which thatcondenser is associated. This means that a 200 k. v. condenser willcontribute only 100 k. v. to the overall constant potential. In order topermit better utilization it is desirable to improve this ratio. Fig. 8shows one arrangement by which this object may be accomplished. (In thisfigure, the resistors 69 to "H are of high value and serve merely toequalize the potential distributions along the two branches of thecircuit.)

In Fig. 8, for reasons shortly to be explained, the peak alternatingvoltage across the condenser and inductance elements is much smallerthan the constant potential developed across each elemental circuitgroup. A a particular example I may refer to the case in which the A. C.voltage attains a magnitude of only 30 k. v. peak whereas the directcurrent voltage attains a value of 100 k. v. For this case the condenserrating need be only 136 kvp, since this is the maximum stress which willbe encountered. In order to charge the condensers to 100 k. v. averageunder these conditions, each of the reactors I0 to It is provided with abooster winding (numbered it to 53 inclusive). The booster winding isassumed to be inductively coupled to the main inductance winding so asto produce a step-up effect by transformer action. The ratio of thewindings should be such that a voltage of 30 k. v. in the maininductance winding will correspond to '70 k. v. in the booster winding.Each of the booster windings is in series with a rectifier connected inshunt to a condenser as in the arrangements previously described.

Since the action of the circuit in the absence of the booster windingwould be to charge the condensers to a peak potential of 60 k. v., theaddition of the booster windings necessarily serves to increase the peakcharging of each condenser to 130 k. v. Since this peak potential isdecreased by only 60 k. v. (2X30 k. v.), at each swing of theoscillating circuit, it will be seen that an average charge of 100 k. v.is maintained on the condenser. A comparison of the peak charge (130 k.v.) with the average charge (100 k. v.) shows that a high degree ofutilization of the condenser capacity is thus achieved.

Fig. 8 also illustrates an arrangement by which .it is possible toenergize the cathodes of the various rectifying devices by abstractingpower from the main resonant circuit. This is accomplished by providingin addition to the booster windings Ill, ll, I2 and I3, additionalwindings ID" to It" inclusive. These are inductively coupled to theother windings referred to so as to be excited thereby. Regulation ofthe cathode heating may be accomplished in each case by the provision ofcontrol resistors numbered 12 to H5 inclusive. These may be controlledby means of a common control shaft I6 indicated in dotted outline.

In similar fashion the cathode 4! of the load device 4|] may beenergized by being inductively coupled to; the resonant circuit. Foreffecting such coupling there is shown a transformer 18 having itsprimary in the resonant circuit and its secondary in series with thecathode 4|. A regulating resistor 79 and a control element 80 thereforare also illustrated.

While I have described my invention in connection with particularembodiments thereof it will be understood that numerous modificationsmay be made by those skilled in the art without departing from theinvention. 1, therefore, aim in the appended claims to cover all suchequivalent variations as fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a resonant circuit containing two similar brancheseach made up of a succession of alternately arranged condensers andinductance elements, the two branches being connested in a closedcircuit so as to have common terminals at their ends, means includingrectifiers associated with the condensers for providing a continuouspath for unidirectional current flowing between said terminals, the saidpath being conductive in one direction only whereby unidirectionalcharging of said condensers is permitted, means for exciting the circuitat its resonant frequency, and means for connecting a direct currentload device to the said circuit terminals.

2. In combination, a resonant circuit having two similar branches eachof which comprises a series of elemental groups made up of alternatelyarranged condenser and inductance elements so correlated as to bemutually resonant, the branches being sequentially connected in a closedcircuit so as to have two common terminals, rectifiers shunting thecondensers of one group so as to permit unidirectional charging thereofand thereby to develop a continuous potential across each of saidelemental groups, and means for connecting a load device to the saidcommon terminals of the two circuit branches so as to subject the deviceto the total continuous potential developed across such branches.

3. In combination, a resonant circuit containing two similar brancheseach made up of a succession of condenser and iron-core inductanceelements, the two branches being connected in a closed circuit so as tohave common terminals at their ends and the corresponding inductanceelements of each branch being paired, a plurality of ferromagnetic coreelements, each forming a common core for one pair of inductanceelements, means for exciting the circuit at its resonant frequency,means including rectifiers associated with the circuit elements toprovide a continuous path for unidirectional current flowing between thesaid terminals, the path being conductive in one direction only wherebyunidirectional charging of said condensers is effected, and means forconnecting a direct current load device to the said circuit terminals.

4. In combination, a resonant circuit containing two similar brancheseach of which comprises a succssion of alternately arranged condenserand inductance elements, the branches being connected in a closedcircuit so as to have common terminals at their ends, rectifiersshunting certain condensers in each branch, means conductive to lowfrequency currents only for interconnecting the two branches atappropriate intermediate points so as to provide in combination with therectifiers a continuous path for unidirectional current between the saidcommon terminals, the said path being conductive in one direction onlywhereby unidirectional charging of said condensers is permitted, meansfor exciting the circuit at its resonant frequency, and means forconnecting a direct current load device to the said circuit terminals.

5. In combination, a resonant circuit including at least two seriallyconnected elemental groups, each of which includes a condenser and aninductance element adapted to resonate with the condenser at aparticular frequency, means for exciting the circuit at such frequency,a rectifier shunting at least one of the condensers to permitunidirectional charging thereof, step-up means in series with the saidrectifier to cause the average potential maintained across the shuntedcondenser to exceed that which it would attain as a result of thecircuit oscillations alone, and connections for impressing on a loaddevice the unidirectional potential developed across the elemental groupwith which the said shunted condenser is associated.

6. In combination, a resonant circuit including at least twoseriallyconnected elemental groups each of which includes a condenser and aninductance element adapted to resonate with the condenser at aparticular frequency, means for exciting the circuit at such frequency,a rectifier shunting at least one of the condensers to permitunidirectional charging thereof, a step-up winding coupled to theinductance element associated with the shunted condenser, meansconnecting the step-up winding in series with the said rectifier therebyto cause the average potential maintained across the shunted condenserto exceed the value which it would attain as a result of the circuitoscillations alone, and connections for impressing on a load device theunidirectional potential thus developed across the elemental group withwhich the said shunted condenser is associated.

7. In combination, a series resonant system comprising a succession ofelemental circuit groups each of which includes a condenser and aninductance adapted to resonate with the condenser at a particularfrequency, means for exciting the system at such frequency,asymmetrically conducting means connected to permit unidirectionalcharging of the condensers thereby to develop a continuous potentialacross each of said groups, and means completing a series circuitbetween the terminals of said resonant system, said last-named meansbeing conductive as to alternating current but non-conconductive as todirect current, whereby the potential appearing between the saidterminals of the resonant system comprises the sum of the continuouspotentials developed across the various elemental circuit groups.

8. In combination, a series resonant system comprising a succession ofelemental circuit groups each of which includes a condenser and aninductance adapted to resonate with the condenser at a particularfrequency, means for exciting the system at such frequency, rectifiersshunting the condensers to permit unidirectional charging thereof, andmeans completing a series circuit between the terminals of said resonantsystem, said last-named means being conductive as to alternating currentbut non-conductive as to direct current, whereby the potential appearingacross the said terminals of the resonant system comprises the sum ofthe continuous potentials developed across the various elemental circuitgroups.

WILLEM F. WESTENDORP.

